1. Field of the Invention
The present invention relates to methods for making structures that mimic the patterns in nanochannel glasses.
2. Description of the Related Art
In complex structures, the relative placement of features is an important concern, along with the size and resolution of the features. It is a continuing goal in miniaturization efforts (e.g., electronics) to make structures, including freestanding (i.e., structures not disposed on a supporting substrate) structures, with nanoscale features (e.g., .gtoreq.10.sup.8, 10.sup.9, 10.sup.10, 10.sup.11, etc. features/cm.sup.2). It is particularly desired to make these structures of various materials that can be used as masks for a variety of parallel processing techniques. Masks made from etched NCG have been used in these processes. However, for feature sizes smaller than 1 .mu.m, the aspect ratio of the etched NCG increases rapidly. For instance, the lowest aspect ratio obtained to date in an etched NCG mask for a 1 .mu.m feature size has been about 4:1 (thickness/feature width). Desirable masks will have controllable aspect ratios.
As used herein, nanochannel glass (NCG) refers to a composite of different glasses, where these glasses are arranged in selected nanoscale patterns. Typically, NCG will be a composite of two glasses, referred to as the "matrix glass" and the "etchable glass". Upon exposure to some agent(s) or condition(s), the etchable glass will dissolve or otherwise be removed from the matrix glass, and the matrix glass will be unaffected, or at least minimally affected by these conditions. Such conditions include, but are not limited to, exposure to a solvent such as an acid, a base, reactive ions, or water. "Etched NCG" refers to the NCG that has been at least partially (and optionally completely) developed by exposure to an agent or condition that will differentially remove glass from the NCG, and "channel" refers to the voids created by this removal of glass, regardless of the geometry of these voids. It is this property of having the different glasses arranged in selected patterns, with high accuracy (ca. 0.5% of channel size), high precision (high repeatability), and small, controllable minimum feature sizes (ca. 10 nm or less), that distinguishes NCG from other composite glasses. Likewise, it is the property of having voids arranged in selected patterns that distinguishes etched NCG from other porous glasses (such as Vycor.TM.).
Currently, conventional high resolution lithographic masks with small feature sizes are made by serial e-beam lithography, or (more recently) by AFM/STM patterning. These require a large number of processing steps, as well as a pixel-by-pixel exposure of the mask.
In particular, it is desired to provide masks for making structures with regular arrays of features, such as quantum electronic devices, magnetic storage media, and nonlinear opto-electronic devices.
For these types of devices with nanoscale features, a continuing obstacle is the inability to combine fine nanoscale features, high packing densities (e.g., .gtoreq.10.sup.9 features/cm.sup.2), and large expanses (e.g., an entire wafer). For instance, in the aforementioned serial e-beam lithography, as the e-beam writing process progresses, there is a tendency for the beam to deviate (or lose global registration) from its intended or programmed location, due to positioning instabilities. This effect can be somewhat mitigated by the use of fiducials, but the problem is inherent to e-beam lithography. In addition to the problem of global registration, long write times are required to write a large number of features. Thus, even if one was willing to go to the (probably prohibitive) expense of trying to expose a large wafer (e.g., a 6" wafer) with a large number of nanoscale features, one would likely find the technical problems insurmountable at present.